In today's wireless communication networks, Public Land Mobile Networks (PLMNs) have been established to provide land mobile telecommunications service to user devices such as electronic book readers, cellular telephones, personal digital assistants (PDAs), portable media players, tablet computers, netbooks, and the like. Generally, each service provider operates its own PLMN, and the number of PLMNs in a country may vary from a single PLMN in a small country to as many as fifty or more in a large country.
Upon initial power up, a user device typically attempts to register with its own service provider's PLMN (the home PLMN). If the user device is located outside of the area covered by the home PLMN, the user device attempts service acquisition on another PLMN, which is commonly known as roaming. Typically, a prioritized list of PLMNs that the user device is allowed to access is stored on a Subscriber Identity Module (SIM) card. The entries and prioritization in the list are usually based on agreements contracted among the various service providers.
When a user device is camped on a PLMN that is not its home PLMN or the highest priority PLMN, the user device usually performs a PLMN scan trying to find its home PLMN or a higher priority PLMN. A PLMN scan is repeated at predetermined time intervals, as defined in a standard specification, such as the 3rd Generation Partnership Project (3GPP) specification. For example, the 3GGP specification requires that a PLMN scan be performed every (6*n) minutes, where “n” is configurable by a service provider and is often set to 1, resulting in a PLMN scan being performed every 6 minutes.
If during a PLMN scan, a home PLMN or a higher priority PLMN is found, the user device immediately sends a request to register with this PLMN. However, if the user device does not find a home PLMN or a higher priority PLMN, the user device continues to perform the PLMN scans every 6 minutes. Such periodic PLMN scans significantly increase current drain of the user device's battery. In addition, if the user device moves to a location where a home PLMN or a higher priority PLMN is present, it would take the user device up to 6 minutes to find that PLMN. For example, if the user device moves to such a location immediately after the last PLMN scan, the user device will not perform the next PLMN scan until the 6-minute time interval expires, thus resulting in 6 minutes of unnecessary roaming charges.